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Shedding Light on the Understanding of High Entropy Alloys

2018.10.15POSTECH IR
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From the cargo ships and airplanes traversing the globe to the automobiles and buildings sprawled throughout the landscape, much of the modern world is built with and upon alloys such as steel. Metallurgists throughout history have passionately struggled to develop novel alloys that are both strong and ductile—properties often diametrically opposed but collectively desired. According to collaborative research conducted by POSTECH and KTH – Royal Institute of Technology, the development of an alloy that surpasses the existing limitation of strength and ductility may soon be possible.

Traditional alloys are usually composed of a main metal, such as iron, and small percentages of different elements, such as carbon. A small percentage of carbon (under 2%) combined with iron produces steel, which is a thousand-fold stronger than pure iron. In contrast to the base element paradigm, high-entropy alloys (HEAs) are new substances that are fabricated with equal or nearly equal quantities of multiple metals, and as such, may have highly desirable properties not found in nature. For example, a popular HEA among researchers is the CoCrFeMnNi, which has been found to have extremely high fracture toughness where both ductility and yield strength increase as the temperature decreases. However, many HEAs with such alluring properties are not thermodynamically stable under normal conditions, and consequently, further in-depth research has been limited.

Professor Se Kyun Kwon from the Graduate Institute of Ferrous Technology at POSTECH and Professor Levente Vitos from KTH used first-principle quantum mechanical tools to demonstrate that a deformation mechanism known as twinning could be precisely controlled to design HEAs with qualities that shatter current limitations. This achievement was published in the world-renowned journal Nature Communications.

Twinning is one of the fundamental modes by which metals and alloys can deform plastically. At the atomic level, alloys are made up of a grid-like structure. Under the appropriate amount of stress, the alloy will deform according to one of the deformation mechanisms. The research team’s theory demonstrated that the control of the specific mechanism is feasible, by which researchers will be able to “facilitate the optical harvesting of their properties.”

Professor Kwon expressed his excitement in applying this new understanding of the plasticity of HEAs to further research on not only designing but developing novel alloys with superb properties for usage in extreme and harsh conditions.

This work was supported in part by the Swedish Research Council, the Swedish Foundation for Strategic Research, and the National Research Foundation of Korea.